Facebook is moving into the hot space of fitness tracking by acquiring a Finland-based mobile app maker.

The social network Thursday said it was acquiring ProtoGeo, based in Helsinki, which makes an activity tracking app for iOS and Android called Moves. The app uses existing technology in people's smartphones, such as the accelerometer, to gather data about people's physical activity as they go about their day.

Calling itself an "activity diary of your life," the app automatically records, for example, walking, cycling and running data, serving up stats like distance traveled and calories burned in the process.

Moves will continue to exist as its own app, so it will occupy a place in Facebook's newly launched strategy around providing a suite of stand-alone apps for specific types of sharing activity. Other apps in this suite include Instagram and Messenger, as well as new apps like Paper, and WhatsApp, pending the closure of that acquisition.

Financial terms of the deal were not disclosed. "As part of Facebook's multi-app strategy, we're excited to announce that the popular Moves app will be joining Facebook's suite of applications," a Facebook spokesman said in a statement. Key members of Moves will be joining Facebook at its headquarters in Menlo Park, California.

"We're joining Facebook's talented team to work on building and improving their products and services with a shared mission of supporting simple, efficient tools for more than a billion people," ProtoGeo said in its own announcement of the deal.

Moves provides information about people's activity similar to how some other physical devices work, like Fitbit, Jawbone's Up and perhaps a new device that Apple is rumored to be developing.

Moves has become a popular app since it launched last year, downloaded more than 4 million times to date for iPhone and Android phones, according to ProtoGeo. Usage of the app could continue to grow as part of Facebook, if people are not scared of what Facebook might do with the data.

Facebook did not say how it might leverage the data gathered by Moves for other purposes -- such as for advertising -- beyond improving people's health.

It's clear Facebook is interested in learning more about its users whereabouts. The company also recently launched a new feature on mobile called "Nearby Friends." That tool, if turned on, tracks the location of users at any given time.